1. Field of the invention
The present invention relates to a pulsed laser control system for controlling a highly repetitive pulsed laser, such as an excimer laser.
2. Description of the related art
Generally, reducing projection aligners (steppers) use laser beams in the ultraviolet range such as excimer laser beams and the like. When a pulsed laser apparatus such as excimer laser device is used in steppers, such apparatus must be controlled for each pulse because highly stabilized laser beam output is required for the steppers.
FIG. 9 shows a general configuration of the laser control system in a conventional pulsed laser apparatus. In FIG. 9, a main controller 102 effects centralized control of devices 121 through 130 constituting a pulsed laser apparatus 102.
The main controller 102 comprises an interface 102i and is connected to an external apparatus 110, such as a stepper, by means of the interface 102i. The external apparatus 110 comprises a controller 111 for controlling the external apparatus 110, and a management device 112 for managing the external apparatus 110 as well as the pulsed laser apparatus 101. The external apparatus 110 and the pulsed laser apparatus 101 are connected by a parallel communication line 103 and a serial communication line 104 such as RS232C.
With reference to FIG. 10, a particular configuration of the laser control system is explained for the case where the external apparatus 110 is a stepper and the pulsed laser apparatus 201 is an excimer laser device. Laser chamber 202 comprises a laser discharge unit LD serving as discharge electrodes in which positive and negative electrodes are arranged in opposition to each other and perpendicularly to this drawing, and laser medium gas comprising halogen gas, noble gas, buffer gas or the like filling the laser chamber 202 is excited by discharge between the electrodes in the laser discharge unit LD so that laser oscillation is effected.
Windows 204 are provided in both laser radiation apertures of the laser chamber 202. Also, a front mirror 205 is provided on the laser beam output side of the laser chamber 202. Further, a band-narrowing module 206 is provided on the side facing a front mirror 205. The band-narrowing module 206 comprises an optical beam-expanding system 20, a mirror 208, a grating 209 that is an angular distributed wavelength selecting element, and a mirror adjuster 210.
An optical cavity is formed between the front mirror 205 and grating 209. The mirror adjuster 210 adjusts the angle of incidence of the laser beam striking the grating 209 by adjusting the angle of the mirror 208. The wavelength selection adjustment of the grating 209 including this mirror adjustment is effected under control by the main controller 230. This control by the controller 230 is effected on the basis of the results of monitoring the laser output beam by a monitor module 220, which will be discussed below.
Laser beam generated in the laser chamber 202 strikes the band-narrowing module 206. More particularly, the laser beam strikes the optical beam-expanding system 207, by which the beam width is expanded in the direction perpendicular to the discharge direction thereof. Furthermore, the laser beam strikes the grating 209 and is diffracted thereby. As a result, only the part of the laser beam with the prescribed wavelength is turned back in the same direction as the incident beam. The beam width of the laser beam turned around by the grating 209 is reduced by the optical beam-expanding system 207 and then the laser beam enters the laser chamber 202. The laser beam is then passed through the laser chamber 202 and amplified. A part of such laser beam is extracted via the front mirror 205 as an output beam, while the remainder is again returned to the laser chamber 202 and amplified.
On the laser beam output side, a beam splitter 211 is provided for splitting a part of the laser beam output from the front mirror 205, so that the laser beam extracted by the beam splitter 211 is input to a monitor module 220. The monitor module 220 detects the beam width, output intensity, and, if necessary, beam profile of the input laser beam, and sends the detected data to the main controller 230. The main controller 230 effects control of the band-narrowing module 206 and the pulsed laser power source device 240 on the basis of these detection results.
When the pulsed laser apparatus 201 actually effects highly repetitive pulsed oscillation continuously, a laser beam emission signal and energy signal are sent from a stepper controller 302. The main controller 230 controls the mirror adjuster 210 and the pulsed laser power source device 240 to cause pulse oscillation based on these signals. This control is carried out for each pulse.
However, in the conventional pulsed laser control system discussed above, all the devices 121 through 130 within the pulsed laser apparatus 101 are controlled in a centralized manner by the main controller 102 only. Therefore, the load is too large for the main controller to effect control for each pulse. In the event that a design change or the like is to be made in the pulsed laser apparatus 101, such load limitations and limitations to expansion hinder construction of an adequate pulsed laser control system and, in addition, considerable work and time are required for the design changes.
Also, in the conventional pulsed laser control system, although centralized control is carried out by the main controller 102, the connections to each device are made by buses between the boards, and a harness is laid round for that purpose. The space within the housing of the pulsed laser apparatus 101 is therefore limited and it is not possible to ensure sufficient space required for the design changes.
Furthermore, because the status log of the pulsed laser apparatus 101 is captured by downloading directly from the pulsed laser apparatus 101, time and efforts are required for the management processing for the pulsed laser apparatus 101.
It is an object of the present invention to provide a pulsed laser control system that resolves these problems, with which changes can be made easily and within a small expansion space, even if design changes are frequently made in the pulsed laser apparatus, and that can easily effect management of the devices constituting the pulsed laser apparatus.
The pulsed laser control system according to the present invention comprises: a plurality of controllers for controlling each of the devices constituting a pulsed laser apparatus; a main controller for controlling the abovementioned plurality of controllers and external apparatus; parallel communication means for parallel communication connections between the abovementioned plurality of controllers and the abovementioned main controller; and serial communication means for serial communication connections between the abovementioned plurality of controllers and the abovementioned main controller by means of a serial network; wherein the abovementioned parallel communication means transmit signals for which realtime performance is required.
With the present invention, the load for controlling the pulsed laser apparatus is distributed among the main controller and the plurality of controllers. Signals for which realtime performance is required are transmitted at a high speed using parallel communication means. The main controller and the plurality of controllers are connected on a network by serial communication means such as Ethernet, for example. As a result, changes involving increase or reduction in [the number of] devices can be handled flexibly and easily.
Also, the space used for the purpose of control within the pulsed laser apparatus is reduced. This can contribute to the realization of compact pulsed laser apparatus.
Furthermore, because the distances of connection from the main controller and plurality of controllers to the devices connected thereto becomes short, good communication can be realized without the need of worrying about the effects of noise or the like.
In the pulsed laser control system according to the second invention, the parallel communication means and the serial communication means are both connected to the external apparatus.
With the second invention, in addition to the operating effects of the first invention, it is made possible to transmit signals, for which real time performance is required, at a high speed from the external apparatus by the parallel connection to the external apparatus. Also, management of the pulsed laser apparatus can be performed remotely because the external apparatus can be connected to a network by serial communication means.